It has already been brought here the idea of being possible to close a tab (when vertical side bar is collapsed) without having to expand it, which, by the way, is an excellent one.
Another thing I find important, is not to allow, when vertical side bar is collapsed, to the upper right close windows button (x), once clicked, to close at once all tabs and the browser. Should be some confirmation (close all tabs?). Thing is it is kind intuitive to hit that close button to close the active tab. Once you do and all your tabs are gone, you realize you've just hit the close window button.
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